This invention relates to the operation of an image forming apparatus, such as, in the case of a photocopying machine, printer, plotter or facsimile machine, wherein images are reproduced by employing a photosensitive, pressure sensitive heat developable film or member and, more particularly, to a color image forming apparatus, such as, image reproducing apparatus, having transport means adapted to control the velocity of the photosensitive receiving member through an exposure station as well as provide for a smooth transport of the member from an exposure station to an image transfer station of the apparatus.
This invention is generally applicable to image forming apparatus wherein the latent image is formed onto a photosensitive receiving member through electrical exposure means, such as, in the case of electronic or electrographic printers, but also is equally applicable to image reproducing apparatus of the type wherein an original image is exposed to a photosensitive receiving member. Thus, as used in this application, "image forming apparatus" relates to any type of such apparatus wherein original images are exposed onto a photosensitive medium. The particular example chosen for explanation of this invention is an image reproducing apparatus is a color photocopying apparatus that utilizes a photosensitive, pressure sensitive heat developable film or member.
An example of a color photocopying apparatus known in the art utilizing a photosensitive, pressure sensitive heat developable film or member is disclosed in Japanese Laid-Open Patent Publication 62-147461. Such apparatus comprises, relative to a defined film transport path, a photosensitive film supply roll, an exposure station wherein the photosensitive receiving film or member is exposed in an image-wise fashion to form a latent image, a heat developing station wherein the photosensitive receiving member is thermally treated to develop the latent image, a pressure transfer mechanism wherein the transfer of a developed image is accomplished from the exposed photosensitive receiving member to an image receiving medium.
In Publication 62-147461, photosensitive receiving member is provided on a supply roll, pulled from the roll and cut into separate sheets of predetermined lengths prior to sequential positioning of the sheets at the exposure station. The sequentially positioned sheets are properly aligned relative to the exposure station and are exposed to a original image to be reproduced. The image may be reflected from an original image and sequentially scanned to form a latent image on the photosensitive receiving member. The development station develops the latent image by heating the photosensitive receiving member to a temperature in the range of about 80.degree. C. to 200.degree. C. for a period of about thirty seconds. The photosensitive receiving member is thereafter advanced to the image transfer station wherein the photosensitive receiving member is aligned and superimposed with an image receiving medium, such as, paper or the like, and the developed image is pressure transferred from the photosensitive receiving member to the image receiving medium. Thereafter, the photosensitive film is separated from the image receiving medium and the spent photosensitive receiving member is guided to a discard bin and subsequently rejuvenated or destroyed.
Because the photosensitive receiving member is severed into individual sheets, a multitude of combination drive and backup rollers are needed throughout the path of movement of the photosensitive receiving member in the apparatus in order to transport the individual sheets along the defined path to and through the several processing stations in the apparatus. The transport system, therefore, comprises drive rollers at the photosensitive receiving member supply roll, the exposure station, the development station, image transfer station and the photosensitive film discard bin in order to properly transport the photosensitive film sheets between and through respective stations. Each drive roller in the system requires a motor or speed reducer as a drive means and a control device to control the drive means. This type of structure and control system wherein a photosensitive receiving member is dispensed from roll type photosensitive receiving member and thereafter cut into predetermined lengths of individual photosensitive sheets results in a complicated and costly drive mechanism structure.
The problems in utilizing an image forming apparatus having a series of photosensitive sheets cut to length has been solved by the employment of a roll type, continuous photosensitive receiving member which is continuously transported between a supply roll and takeup roll in the image forming apparatus remaining in its uncut state. However, further .problems are introduced and encountered in the transport of a continuous photosensitive receiving member which require further attention. First, it is essential to maintain the transport velocity of the continuous photosensitive receiving member through the exposure station at a constant rate. Otherwise, since the exposure of the original image and its scanning onto to the moving photosensitive receiving member is being carried at a predetermined scanning rate, any change in the rate of movement of the photosensitive receiving member transported through the exposure station will bring about the formation of distortion in the latent image formed on photosensitive receiving member.
Secondly, in the case wherein the drive means at the exposure station is linked to the drive means at the image transfer station in order to maintain a constant transport velocity concurrently through both of these stations, the transport rate of movement of the photosensitive receiving medium through the exposure station as compared through the image transfer station will differ due to (1) the stretching or shrinkage of the photosensitive receiving member as it is transported through the thermal operated development station, (2) the physical expansion and contraction of the drive roller itself occurring at the image transfer station or (3) image transfer under a pressurized state in conjunction with the image receiving medium in the image transfer station. Therefore, a significant tension state is brought about to the photosensitive receiving member between the exposure station and the image transfer station resulting in slack condition produced on the member which causes the member to become unevenly developed and/or jamming of the member along the transport path. Therefore, it is necessary and desirable to eliminate or control any slack condition of the photosensitive receiving member in addition to providing a slower transport velocity at the image transfer station compared to the transport velocity at the exposure station.
It is an object in this invention to provide an enhanced primary transport system for a photosensitive receiving member of a continuous length through an image forming apparatus.
It is another object of this invention to provide an enhanced transport system for a photosensitive receiving member of a continuous length through an image forming apparatus comprising a primary transport system and a secondary transport system with a differential motion buffer provided between these systems.
It is a further object of this invention to solve the foregoing problems by providing a simplified transport system of a photosensitive receiving member through an image forming apparatus capable of maintaining a constant velocity in the transport of the photosensitive receiving member through the exposure station while providing smooth, continuous transport of the photosensitive receiving member from the exposure station to the image transfer station without causing undesirable slack, wrinkling or jamming of the photosensitive receiving member, or causing distortion in the developed image transfered to the image receiving medium.